1. Field of the Invention
Embodiments of the invention generally relate to a substrate support adapted to retain a liquid on its surface.
2. Background of the Related Art
Integrated circuits have evolved into complex devices that can include millions of transistors, capacitors and resistors on a single chip. The evolution of chip design continually requires faster circuitry and greater circuit density that demand increasingly precise fabrication processes. Two fabrication techniques becoming more frequently used during chip fabrication are plating and electrochemical polishing.
Plating techniques are generally used to deposit conductive materials on a substrate surface. One plating technique is electroless plating. In general, electroless plating is performed by covering a surface with a solution containing metallic ions. The metallic ions attach to the surface through a chemical reduction reaction without the use of electricity. Another plating technique is electroplating. In general, electroplating is performed by applying an electrical bias between an anode and a substrate surface. Conductive material, either from the anode or from an electrolyte solution used to form a conductive path between the anode and the substrate, is deposited on the substrate surface. During plating, the substrate is often rotated or agitated to enhance uniformity of the deposited material.
Electrochemical polishing techniques are generally used to remove conductive material from a substrate surface by electrochemical dissolution. Electrochemical polishing often includes mechanically polishing the substrate with reduced contact force as compared to conventional chemical mechanical polishing processes. Electrochemical dissolution is performed by applying an electrical bias between a cathode and a substrate surface to remove conductive materials from a substrate surface into a surrounding electrolyte used to form a conductive path between the substrate and the cathode. During electrochemical dissolution, the substrate is typically placed in motion relative to a polishing pad to enhance the removal of material from the surface of the substrate.
Systems that perform plating and electrochemical processes may retain the substrate in a face-up orientation during processing. In these systems, the substrate is supported on a platen that is disposed in a basin adapted to hold an electrolyte solution. For electrically driven processes, an electrode (i.e., an anode or cathode) is disposed above the substrate. The basin and platen are flooded with enough electrolyte to establish a conductive path between the electrode and the substrate. A bias is applied between the electrode and the substrate and an electrochemical process (i.e., electroplating and electrochemical dissolution) is performed on the substrate.
As the basin is typically much larger than the substrate being processed, a large volume of electrolyte is utilized to cover the polishing surface and maintain the current paths. High usage of electrolyte contributes to excessive costs of process consumables. As chip fabricators are tending towards processing substrates of larger diameters, the cost of consumables continues to undesirably increase.
Moreover, electrolyte may not always be effectively removed from substrates processed in a face-up orientation, resulting in surface contamination of the substrate. Additionally, if the electrolyte is not removed from the platen after processing, electrolyte may wet the substrate supporting surfaces of the platen after the substrate is removed. Electrolyte, drying on these surfaces, becomes a potential source of substrate scratching and particle generation. Furthermore, if the substrate supporting surface includes electrical contact pads used to bias the substrate, the electrolyte may etch, attack, corrode or deposit on the pads, thus degrading uniform current transfer and disrupting process uniformity across the diameter of the substrate.
Therefore, there is a need for an improved substrate support.